With the seemingly regular occurrence of oil tankers running aground and dumping their contents into the world's waterways and inland fuel spills contaminating acquifers and soils, there has been a significant amount of activity in the oil spill clean-up art. Various methods have been set forth in an attempt to contain the oil once the same is spilled in order to prevent damage to aquatic life and other aspects of the environment. Chemical additives, porous materials, as well as various sheets and barriers have been proposed in the prior art, typical of the latter being U.S. Pat. No. 5,120,598, issued to Robeson et al. Jun. 9, 1992. The Robeson et al. disclosure provides a mat product composed of polyvinyl alcohol ultra-fine fibers. The same are formed into a mat and the mat is brought into contact with the oil spill. The result is that the fibers adsorb the oil.
The Robeson et al. arrangement, although a meritorious and useful product, still requires removal from an oil slick once the fiber mat is saturated. In addition, presumably the oil must be removed from the mat before the same can be used in a similar manner. Clearly this is a cumbersome procedure and costly from a time point of view. One expects similar difficulties with other mats and adsorbent.
Nohmi et al., in U.S. Pat. No. 4,229,297, teach a method of separating oil from an oil containing liquid. This reference is generally useful for oil separation, however, there is an inherent limitation in the Nohmi et al. methodology. The reference indicates that the mixture may be separated into distinct phases by forcing the mixture into contact with the inside surface (lumen) of the microporous hydrophobic hollow fibers. In this regard, the flow in the Nohmi et al. reference is referred to as "down-bore". This refers to the fact that the two phase mixture is forced down the lumen of the fiber as opposed to being passed into contact with the outside surfaces of the fiber, i.e. shell side feed. It is known in the art that it cannot be predicted what the pressure drop over a given length of fiber will be for a two-phase down-bore feed as in the feed type in the Nohmi et al. reference. Additionally, there is an absolute maximum amount of water which can be fed per fiber, above which "water breakthrough" occurs. Accordingly, the Nohmi et al. teachings would not be useful to one trying to recover as much water free oil as possible from an oil/water feed without exceeding the pressure at which water and oil both permeate through the fiber walls (water breakthrough). When the water breakthrough pressure is reached, it is no longer possible to obtain the desired result(s), water free separate phase oil and simultaneously oil free separate phase water.
U.S. Pat. No. 5,073,261, dated Dec. 17, 1991, and issued to Conradi et al., provides a collapsible container having an inlet and an outlet and being composed of a water impervious rubber material. The collapsible container is connected to an inlet for charging an oil-water mixture into the container. The container is configured with baffles, etc., to specifically contain the oil therein, the oil container subsequently being towed to a further location for removal of the oil. This arrangement does not result in the immediate removal of the oil from the water body containing the oil spill, but rather separates the oil from the water body containing the same while the container, having the oil therein, is still in the water. There is therefore, a possibility that residues may remain on the water surface even though a substantial amount of the oil is contained within the container floating in the water.
Cote et al., in U.S. Pat. No. 5,248,424, issued Sep. 28, 1993 provides a further variation on hollow fiber separation technology. The reference discloses the use of hollow fibers for separating various compounds. The Cote et al. arrangement has been designed to handle solid particulate removal from an aqueous mixture as opposed to liquid-liquid separation. This is further evinced by the fact that the Cote et al. method involves the pretreatment of the hydrophobic fibers to render them hydrophilic. This is an absolutely essential step in the manufacture or the pretreatment regime. In a situation where the Cote et al. arrangement were used to separate oil, the oil would eventually permeate through, along with the water, into the fiber thus negating the purpose of separation.
In view of the structure of Cote et al. and together with the teachings in the disclosure, it is clear that the Cote et al. arrangement and method would not be adequate for separation of an organic liquid disposed within an aqueous medium. In several embodiments, the fibers are essentially unsupported and are disposed in arcuate relationship with one another. Such an arrangement has effect in only certain limited conditions. The arrangement would not be effective in, for example, an oil spill situation on a large body of water. The Cote et al. reference makes no provision for fiber dimensional changes which occur when the fibers are in contact with, for example, oil. In this situation, the Cote et al. arrangement would simply "bundle" or "clump". This inherently leads to efficiency limitations since the available area of the fibers is reduced and, therefore, the degree of contact with the mixture is reduced. Accordingly, it is clear that the teachings of the Cote et al. only relate to non-oil based separations.
Taylor, in U.S. Pat. No. 4,886,603, teaches a separation method where diesel oil contaminated with water can be apparently dewatered by pumping the mixture which is an emulsion or solution through the lumen of microporous polyvinyledene fluoride (PVDF), hollow fiber modules capable of separating the oil as the permeate. The arrangement employed to facilitate this separation is a two-stage hydrophobic microporous hollow fiber module. In the Taylor teachings, it is clear that the Taylor reference relies on forcing an emulsion or solution of oil in water down the lumen of the hollow fibers in order to apparently achieve separation of the oil from the water. Since the Taylor reference is directed to emulsified and soluble oils and therefore, the Taylor reference achieves only a partial recovery of the permeate which is water-free oil in a single step and requires the passage of a retentate into a second chamber equipped with a hydrophilic membrane in order to recover free phase water. Notably, neither step achieves quantitative separations. The Nohmi et al. drawbacks hereinbefore detailed apply equally to Taylor discussed hereinbefore and Ford discussed hereinafter.
A further reference which teaches separation of organic aqueous mixtures is Ford, in U.S. Pat. No. 4,846,976. The Ford reference makes the point that oil removal from an oil-water mixture is best conducted if the mixture is forced through the lumens. In this regard, the Ford teachings are quite similar, from a broad point of view, to those in the Taylor and Nohmi et al. references and as such, the teachings of Ford have inherent problems with permeate quality in terms of efficiency of phase separation without contamination.
There has been a significant amount of work performed in this art, resulting in a significant number of patents related to the instant invention. The following represents a list of patents forming a portion of the body of the United States prior art in this field. U.S. Pat. Nos. Re. 31,087, 2,523,091, 3,487,927, 3,669,275, 3,737,043, 3,872,014, 4,126,556, 4,172,039, 4,197,204, 4,371,441, 4,469,170, 4,663,037, 4,668,401, 4,670,156, 4,772,390, 4,897,191, 4,902,418, 4,944,877, 5,013,437, 5,094,750, 5,151,191, 5,169,529, 5,169,530, 5,174,900 and 5,183,566.
Other generally related art includes Canadian Patent Nos. 1,221,645, 1,245,567, 1,290,257, 1,323,582, 2,007,917, 2,027,114, 5,202,023, 5,207,906, 5,209,852, 5,225,079, 5,282,975, 5,352,361, 5,429,742, and 5,480,553.
In view of what the prior art has proposed as possible solutions for cleaning up oil spills and removal of organic materials which may be environmentally hazardous, there clearly exists a need for a more advanced system which is capable of removing and recovering the organic material from an aqueous system which is efficient, reliable and results in substantially complete separation of the organic phase from the liquid phase without contamination of one phase within the other. The present invention clearly addresses the solution to this problem and satisfies the desirable result of producing discrete and substantially pure phases.